As a common practice for dissipating heat from a modular power supply, a heat sink is combined with the modular power supply, and the heat sink closely contacts some heat-producing elements, so that heat is conducted to the heat sink and then to the outside. In addition, there are certain requirements for insulation and enhanced insulation in the modular power supply.
The designs of heat dissipation and insulation in the prior art have the following drawbacks. Thermal resistance between the power components and the heat sink is large, and the heat dissipation is poor. The heat sink is complicated in structure. It is difficult to deal with the isolation between the modular power supply and the heat sink.
Reference is made to FIG. 1, which illustrates a structural view of a modular power supply in the prior art. An irregular heat sink 300 is engaged with power components 100 which are mounted on a printed circuit board 200, with heat-conducting glue 400 being filled therebetween. The arrows indicate the direction of heat conduction. Heat from a magnetic element in the power components 100 is conducted to a bottom of the heat sink 300 via the heat-conducting glue 400 and then via an insulating layer 500. Heat from a semiconductor device in the power components 100, e.g., a switching device (like an insulated gate bipolar transistor, IGBT) is firstly conducted to a top of its case, and then to the heat sink 300 via the heat-conducting glue 400 and the insulating layer 500. Taking a switching device (e.g., an IGBT) packaged by Power pak so-8 (PPAK-SO8, 5 mm*6 mm) which is produced by Infineon as an example, the prior art at least suffers from one of the following drawbacks.
1. Thermal resistance between hot sources of semiconductor devices in the power components 100 and the top of the case is very large (>15° C./W).
2. Since power components 100 are of different heights, there are many steps in the heat sink 300. As a result, the heat sink 300 is complex in structure, and it is difficult to deal with the isolation between the heat sink 300 and a module. Generally, an insulating layer is required for each platform, and steps are required to overlap with each other. However, requirements regarding insulation probably can not be met in this case.
3. Generally, the number of steps in the heat sink 300 is controlled to 2 or 3. In this case, the power components 100 from which heat can be dissipated directly via the heat sink 300 are limited in number.
4. Due to the tolerance in height of the power components 100, it is required to fill a gap between the heat sink 300 and the power components 100 with the heat-conducting glue 400. Thermal resistance will be increased to a certain extent. For example, heat-conducting glue with a thickness of 0.3 mm has thermal resistance of about 5.5° C./W.
5. Since there is a distance between the heat sink 300 and the printed circuit board 200, heat from the printed circuit board 200 can not be dissipated directly via the heat sink 300.
6. Generally, power components 100 are disposed on both surfaces of the printed circuit board 200. In this case, there is no path for the heat from power components 100 on one of the surface to be dissipated directly to the heat sink 300.